History of British animals - University of Guam Marine Laboratory

Tethya. ZOOPHYTA. SPONGIAM:. 519of horny fibres, as the species so commonly used for domestic purposes; or compound, being strengthened bycalcareous or siliceousspicula.The gelatinous matter, abounding in transparent globules,connects the different partsof the skeleton, lines the various canals,and forms the margins of the openings. The pores are minute openingswith a gelatinous margin, strengthened or defended by the skeletonor spicula,into which the water enters in currents,generated probablyby a ciliary apparatus which has not yet been perceived by themicroscope. The water, after traversing the interior canals, is ejectedby means of orifices, which are larger than the pores, and in many speciesare elevated above the surface, in the form of perforated papilla?.The ova are numerous, at first appearing like groups of minute, irregular-shaped,opaque granules, derived from the gelatinous matter, whichunite into ovate bodies, falling at maturity into the canals, and expelledby the orifices. These ova float in the water, and exhibit spontaneousmotion by the rapid action of the cilia?, which cover the anterior portionof the body, and at lengthattach themselves, and then expand intothe forms of maturity.The currents from the orifices are best exhibited by placing the recentanimal in a shallow dish of water,and throwing a littlepowderedchalk on the surface, the motions of which will indicate the directionof the streams. For the purpose of examining the skeleton, it is requisiteto macerate the sponge in hot water, which removes the gelatinous matter,and leaves the remainder in a state fit to be examined under a microscope.When the spicula are siliceous, the animal matter maybe removedby nitric acid or by combustion, as was practised by Muller(Zool. Dan. t. lxxxv.), when the vitreous needles will appear unaltered.In examining cabinet specimens of sponges, care must be taken tomake allowance for the degree of maceration they may have undergone,as, upon this circumstance, their porosity, friability,or softnessdepend.Gen. XLII. TETHYA.— Hemispherical, with numerous fibresradiating from the centre to the surface,and consisting oflinear, fusiform, siliceous spicula.— An intermediate genusbetween Cydonium and IJalichondria.91. T. cranium.— Surface regular and closelyvillous.Alcyonium cranium, Mull. Zool. Dan. t. lxxxv. f. 1—A. Lyncurium,Jameson, Wern. Mem. i. 563— Spongia pilosa, Mont. Wern. ii. 1 19,t. xiii. f. 1, 2. — Adheres to stones in deep water, Zetland, where it istermed Sea-Apple.